The present invention relates to a transmission device, and relates more specifically to a transmission device suitable to measurement of the pressure or the pressure difference between two points of a fluid of a nuclear plant, oil refinery plant, chemical plant and the like and to transmission of the detected signal thereof.
The transmission device is for transmitting the pressure of a fluid received by a diaphragm to a sensor by a sealing liquid sealed in a pressure leading passage and transmitting the electric signal detected by the sensor to the outside, and there are two kinds of one measuring the absolute pressure and one measuring the pressure difference.
These pressure and pressure difference transmitters are used in a nuclear plant, oil refinery plant and the like, and, from the viewpoint of securing safety of the plant and securing the quality of the product, the accuracy of ±1% for example is required. However, due to the influence of hydrogen permeated from outside the pressure and pressure difference transmitter, it was difficult to maintain the accuracy for a long period of time.
More specifically, because a part of hydrogen (hydrogen molecule, hydrogen atom, hydrogen ion) contained in the measured fluid stays as bubbles in the sealing liquid filled in the pressure leading passage after permeating the diaphragm, by the effect thereof, the pressure inside the pressure leading passage rises, the change of the pressure applied to the diaphragm cannot be correctly transmitted to the sensor, and the measurement accuracy deteriorates.
Therefore, in the past, as described in JP-A-2005-114453 for example, hydrogen permeating the diaphragm of the pressure receiving section from the outside was suppressed by arranging a hydrogen occluding film on the sealing liquid side of the diaphragm. Also, a similar technology is described in JP-A-2004-361159.
However, according to the technologies described above, there were problems that the sealed amount was limited as a hydrogen occluding material and that, because the specific surface area was comparatively small, the effect of reducing the influence of hydrogen and a hydrocarbon group generated inside or hydrogen having permeated from the outside was not sufficient.